In the field of oil drilling and excavation, the bottom-hole refers to the base of the well. Accurate bottom-hole data is important to manage the reservoir and to ensure that a well is enabled to deliver more oil. Additionally, accurate bottom-hole data can be used to increase the efficiencies in production planning and recovery. Therefore, it is desirable to be able to obtain accurate bottom-hole data as decisions on the productivity of a well are made using such data.
Phase redistribution is observed in oil and gas wells during shut-in, where the oil and gas separate in the wellbore. An example of the physical characteristics of a well in steady-state and shut-in are shown in FIG. 6. The accuracy of pressure change calculation during shut-in depends on how accurately the gas and oil mixture gradient are modeled. A parameter of the fluid mixture gradient is the distribution of gas and liquid phases in the wellbore.
If a good dynamic well model can be built to describe the complex mechanisms occurring during the transient well shut-in period from the semi steady-state well flowing period, some key well parameters can be obtained with more certainty. These parameters would include the reservoir pressure, well productivity index and skin, giving the operator great economic benefits.
However, the acquisition of bottom-hole data can be difficult and expensive. It is known to obtain bottom-hole data from permanent downhole gauges or through well intervention measurement. However, permanent downhole gauges are often expensive and unreliable whereas well intervention measurements are by their very nature are intrusive. Furthermore, the use of well intervention measurements often leads to well downtime to remove the often stuck instruments inside the well, or in a process known as “fishing”.
It is also known to use PVT (pressure, volume, temperature) modeling, along with surface data, in order to provide an estimate of the conditions within the well. However, such models are known to be of limited accuracy. In particular they are unable to model the phase transitions in wells accurately as they assume an instantaneous phase transition between gas and oil.
In a shut-in well, one which has closed off, unlike a producing steady-state well, phase distribution is known to occur, where the gas and oil separate. By accurately modeling the transition, accurate values of key parameters such as reservoir pressure may be obtained. However, unlike during the steady-state of the well, the contents are undergoing a phase transition making the modeling considerably more complex.
During the 11th European Conference on the Mathematics of oil recovery, September 2008, a paper was presented by Hon Vai Yee et al., outlining a workflow for subsurface data determination. The present invention discloses improvements to the workflow in order to model more accurately the bottom-hole reservoir pressure.
Therefore, it is an object of the invention to provide a non-evasive method of determining the physical parameters within a shut-in well, in particular the determination of the bottom-hole reservoir pressure.
In order to mitigate at least some of the above problems, there is provided a computer implemented method according to claim 1.
Further aims and aspects of the invention will be apparent from the appended claims.